Resistance-wire for electric heaters.



R. H. READ.

RESISTANCE WIRE FOR ELECTRIC HEATERS.

APPLICATION FILED JULY 11, 1914.

1,127,281. Patented Feb. 2, 1915.

Wummm I M W \M of economical operation.

UNITED STATES PdTFENT OFFICE- ROBERT H. READ, OF WASHINGTON, DISTRICT OFCOLUMBIA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEWYORK.

RESISTANCE-WIRE FOR ELECTRIC HEATERS.

Specification of Letters Patent.

Original application filed July 19, 1910, Serial No. 572,778. Dividedand this application filed July 11, 1914.

Serial No. 850,489.

lated resistance wires or elements for electric heaters or the like andis applicable in all cases where electrically generated heat is utilizedor dissipated. The heating wire is of a type comprising a highresistance corewire inclosed in a continuous metallic shell or armor andseparated therefrom by a firmly packed annular layer or bed of mineralfireproof insulation in the form of powder. Such wires are alloysvarying in speoific resistance, but always very high relatively to agood conductor such as copper, and are therefore adapted for heatingwork or such as requires a large diffusion or dissipation of energy ascontradistinguished from ,conducting' work where a minimum dissipationof energy is required for reasons v With a mineral oxid insulation suchas ground flint the temperature may be raised very high, as suchsubstance has a melting point above 2,000 centigrade and isnot at alldamagedby temperatures below its melting point. Ground flint, magnesiaand many other oxide or compounds do not become conductive when heated,the melting point being so high that they do not become conductors ofthe second class (Nernst eflect) except at very high temperatures. I mayuse any highly refractory insulating powder; I prefer, however, to useground flint, such as ground quartz or silex because of its cheapnessand better thermal conductivity than other oxids or silicates, and whichinsures a quicker and more desirable operation for heater or rheostatwork. Other mineral oxid powders such as magnesia, alumina, emery,orsulfates, or carbonates such as chalk,-or silicates such as soapstone,clay or asbestosmay be employed. The powder should be finely divided,free from granules to permit even distribution, and should pack well,preventing the infiltration of air. I have had excellent results with aform of oWder-lmown on the market as silex, WlllCll is sold as apolisher of metals, and is finely divided silica; a good quality ofpowder may be made by grinding flint finely and then separating thefiner particles by levigation. Before using, it should be heatedstrongly to expel all moisture. A finished corewire of high resistancealloy such as German silver, Climax, or a nickel chronium alloy issurrounded with the powder and telescoped within a seamless tube ofmetal with a good clearance around the wire and powder and is thenreduced in section. The armor may be of the same material as thecore-wire or a metal of the same expansion coefficient so as to avoidstrains clue to differences in expansion under heat of the core andshell, or in some cases may be of copper or low brass. I provide aterminal to guard the core-wire when sharply flexed from contact withthe jacket. This may be done by laying bare the core by removing a shortpiece of the jacket, using preferably a revolving knife such as a smallpipe-cutter. A piece of copper wire may be welded to the ends of thecore-wire,

and a metallictube filled with powdered flint or with cement pushed overthe wire until it bears on the shell. It may be sol-- dered or brazed tothe shell, thus making a rigid structure. The powder fills the tube andcarries the heat away from the wire, and the copper will not get hot andmay therefore be led directly to a binding post or other circuitterminal. Thus I have an armored or sheathed wire in which the shelloffers a large surface of exposure to the air or other heat absorbingmedium, permitting the passage of a greatly increased current withoutoverheating and maintaining the resistance core cool throughout itslength.

This application is a division of my application #572,778, filed July19, 1910 entitled Insulated conductors and process and apparatus formaking the same.

In the accompanying drawings, Figure 1 shows enlarged an armored wirepowdercovered and surrounded by a seamless metallic jacket; Fig. 1*- isa cross-section of the same; Fig. 1 shows the wire reduced until thejacket is firmly shrunk upon the filled or covered wire; Fig. 1 showsthe wire much reduced under the action of rolls or dies; Fig. 2 shows astep in the preparation of the heater wire; and Fig. 3 shows theterminal used at the ends of the heater wire.

Patented Feb. 2, 1915.

A metal ribbon or tape is passed to a curling die which gradually formsit into a tube, and at the open end is supplied with previ ously heateddry insulating powder of the kind referred to, precautions being takento provide a uniform supply of the powder as the tape is formed into atube. A corewire of high resistance alloy' is led axially of the tubebeing filled and at the same speedof travel. Means are provided forkeeping the seam in a right line, as a blade of steel 8 at the front ofthe die. The seam may be brazed or welded, but good results may beobtained without this treatment, as a seamless outer shell of the properclearance effectually prevents leakage of the powder, by closin tight onthe inner folded metal tape an preventing any tendency to I .ooze at theseam., The filled tube is slipped into a seamlessv metallic tubepreviously drawn down to a size to permit it to be easily slid ortelescoped intoit. The structure thus provided is then drawn down indies or otherwise reduced until the desired size is attained, when thepowder will be hard packed and the core-wire central. vAs will be seenin Fig. 1 there is a good clearance between the seamless jacket and thepowdercovered wire core. In Fig. 1 the jacket has been reduced and hasbeen shrunk into intimate contact with the covered wire, while in Fig. 1the whole has been very much reduced in section. Such a wire may bereduced or drawn down to a very few thou sandths inch in diameter.

I provide a terminal at the end of the core-wire so arranged as toprovide effective 'radiation for'the heat and to prevent metalliccontact with the jacket. A simple and effective plan is to lay barethecore by removing a short piece of the jacket, using preferably arevolving knife, such as a-small pipe-cutter. A piece of copper wire maybe welded to the end ofthe core-wire and a metal tube having a porcelainbead shrunk in the end and filled with powdered flint or cement, as at1, slipped over each end of the shell, thus making a rigid structure.The powder fills the tube and carries the heat away from the wire, andas'the'copper "will not by reason of its low resistance get hot it maybe led directly to a binding post or other circuit terminal. If brazedseams are'used the solder should have a sufficiently high melting pointto permit annealing, or the seam should be welded or burned in anapproved manner. v

I do not claim in this application a corewire of high resistance in aseamless tube with closely compacted powder insulation and a seamlessmetallic shell on the outside, such matter being claimed in my copendingapplication #841,544, filed May 28, 1914, nor do I claim means forexcluding moisture which is claimed in my application #843,236, filedJune 5, 1914, nor do I claim inclosing a wire with powder insulation ina Having thus described my invention, what I I claim as new and desireto cover by Let ters-Patent is 1. Aninsulated resistance wirefor-electric heaters or the like comprising a corewire of highresistance material, a body of heat refractory powder compacted aroundthe core-wire, a metallic armor surrounding the insulation, and aterminal of higher conductivity than the core-wire forming acontinuation thereof partly embedded in the powder. 1

2. A resistance wire for electric heaters or the like comprising acore-wire of high resistance alloy, a body of heat refractory insulatingpowder surrounding the corewire, a metallic armor inclosing the powder,and a terminal of higher conductivity than the core-wire embedded in thepowder and projecting from the armor to carry away the heat and form arelatively cool extension thereof.

3. A resistance wire for electric heaters or the like comprising a highresistance corewire, a filling of heat refractory insulating 5. Aresistance wire for electric heaters.

or the like comprising a high resistance corewire, a compact body ofheatrefractory insulation surrounding the same, a metallic shellinclosing the same, copper wires metallically united with the'ends ofthe corewire projecting from the shell and partly inclosed within thebed of insulation.

6. A resistance wire for electric heaters or the like comprising a highresistance corewire having terminals of lower resistance, a compact bodyof. heat refractory insulation surrounding the same, a seamed metallicinclosure for the powder, 'a seamless metallicshell on the outside, andmetallic. caps at the ends insulated, from the corewire and covering thepoint of decreased resistance.

7. The method of making a resistance element for electric heaters or thelike, consisting in surrounding a core-wire with insulating powder,inclosing it within a metallic sheath, reducing the section of thesheath, and providing terminals of lower re sistance at the ends of thecore-wire extending within the powder insulation.

8. The method of making a resistance element for electric heaters or thelike, consisting in surrounding a high resistance core-wire withinsulating powder, inclosing it within a seamless metallic shell,reducing the cross section of the whole, and providing it with terminalsof lower resistance than the core-wire extending from a point within thepowder insulation.

9. The method of making a resistance element for electric heaters or thelike, consisting in surrounding a high resistance corewire withinsulation, inclosing it within a loosely fitting seamless metal tube,shrinking the tube on the insulation, cutting off the ends of the tubeto expose the core-wire, providing terminals of lower resistance for thecore-wire, and surrounding the points of lower resistance with heatabsorbing material to prevent overheating.

10. A resistance wire for electric heaters or the like, comprising ahigh resistance core-wire, a metal tube surrounding the same, a fillingof heat refractory insulating powder between the two, a metallic capforming a prolongation of the tube filled with insulating heatrefractory material, and a terminal of better conductivity secured tothe core-wire within the cap.

11. A resistance element for electric heaters or the like comprising ahigh resistance core-wire, a metal tube surrounding the same, a fillingof heat refractory powder between the two, a terminal of betterconductivitv than the core-wire at each end, and a perforated insulatingbead to hold the wire central.

ROBERT H. READ. Witnesses:

E. B. MCBATH, S. C. HILL.

